Controllable inductor



1961 e. s. DICKINSON CONTROLLABLE INDUCTOR Filed Dec. 6, 1955 FIG. 2.

FIG. 5.

INVENTOR'. GEORGE $.DICKI nsou United States Patent 2,996,695CONTROLLABLE INDUCIOlR George S. Dickinson, Fairfield, Conn., assignorto C.G.S. Laboratories, Inc., Stamford, Conn., a corporation ofConnecticut Filed Dec. 6, 1955, Ser. No. 551,267 6 Claims. (Cl. 336-155)This invention relates to controllable inductors in which the inductanceof a signal winding is varied by changing the degree of magneticsaturation of ferromagnetic cores by changing the magnitude of a directcurrent through a separate control winding.

The invention relates particularly to the configuration and arrangementof the various parts of the core structure by which an inductor isprovided capable of controlling audio and radio frequency signals. Theresulting unit is particularly advantageous in that it has lowdistributed capacity in the signal winding, minimum hysteresischaracteristics, and low residual magnetism. The various features of theinvention will be apparent from the following description .of acontrollable inductor embodying the invention considered in conjunctionwith the accompanying drawings, in which:

FIGURE 1 is a diagrammatic perspective view of a controllable'inductorembodying the invention; I

FIGURE 2 is a sectional view taken along line 22 of FIGURE 1;

FIGURE 3 is a sectional view taken along line 33 of FIGURE 1;

FIGURE 4 is a plan view of part of the laminated core;

FIGURE 5 is a plan view of the other part of the 1aminated core; and

FIGURE 6 is a perspective view of the inductor mounting bracket, thewindings being omitted to simplify the illustration.

As shown in the drawing, the controllable inductor includes an H-shapedyoke generally indicated at 2, formed of soft iron laminations. Acontrol winding 4 is positioned around this yoke 2 and is more or lessin the shape of a ball so that the maximum number of turns can bepositioned within a ring 6 formed of ferrite material. The winding 4need not -fill all of the space within the ring 6 and usually it ispreferred to leave substantial space between the winding 4 and the ring6. The ring 6 extends through the opposite end portions of the H-shapedyoke and carries a signal winding 8 which is wound in two parts,indicated respectively at 8a and 8b, and which are connected in series.

In use, the circuit to be controlled is connected to the leads 10 and 12of the signal winding 8. A source of variable D.-C. current is connectedto the control winding 4. With zero control current in the winding 4,the signal winding has maximum inductance. As the control current isincreased, the ferrite core ring 6 becomes partially saturated with acorresponding decrease in the inductance of the signal winding 8. Withcomplete saturation of the core ring 6, the signal winding reaches itsminimum value of inductance.

The yoke 2 is formed of a first set of rectangular laminations indicatedat 2a, and a second set of laminations indicated at 2b, which areprovided with a step at each end. The shorter length dimension of theselaminations 2b is arranged to be slightly less in length than the insidediameter of the core ring 6, and the longer dimension of the laminations2b is equal to the length of the laminations 2a, which is in turnapproximately equal to the outside diameter of the ring core 6.

In assembly of the unit, the control winding 4 is most convenientlywound on a conventional rectangular bobbin with the center portion ofthe winding bellied out so Patented Aug. 15, 1961 as to fit nicelywithin the core ring 6. The lamination 2b are then placed within thebobbin of the control winding which is then positioned within the ring6. The other set of laminations 2a is then pushed longitudinally throughthe remainder of the opening in the control winding bobbin to form theH-sh-aped yoke as illustrated in the drawing.

After assembly, the yoke 2 may be held in place merely by frictionalcontact with the inside of the control winding 4, but it is better toclamp it in place mechanically by any suitable means or by cementing it.In order to insure that firm contact is made between the yoke 2 and theinner surface of the ring 6, every other lamination of the set 2b isforced longitudinally in one direction and the intervening laminationsare forced in the opposite direction. This is most readily accomplishedby the unsymmetrical structure of the core laminations 2b. Thus, asindicated on a magnified scale in FIGURE 4, the dimension indicated at2e is shorter than the dimension indicated at 2 When the laminations arestacked, they are stacked in alternate direction; that is, with one ofthe extensions 2e adjacent the extension 2 of the next lamination.Therefore, when the unit is finally constructed, it is only necessary toapply compression to the end surfaces 2g of the laminations 2b to forcethem into engagement with the inner surface of the ferrite ring core 6.Thus, as shown in FIGURE 3, the right end 20 of each alternatelamination 2b is forced against the inner surface of the ring 6 and theopposite end 2d has a slight air gap, and, conversely, the left end 2dof each intervening lamination 2b is forced in the opposite directionagainst the inner surface of the ring 6.

FIGURE 6 shows one form of structure which can be used to support theinductor. Two channel members 16 and 18 of brass or other suitablematerial are positioned along opposite edges of the core 2 inside thecontrol winding 4. These members are clamped together at one end by ascrew 20 and at the other end by a screw 22 which extends also throughthe lower portion of a U-shaped bracket 24. The lower ends of thebracket 24 are soldered to a base 26. The upper ends of the channelmembers 16 and 18 are secured to the bracket 24 by soldering or othermeans.

It will be seen that in accordance with the invention, there is provideda controllable inductor that is small in size, and which can befabricated economically, and which is well adapted to meet the ends andobjectives hereinbefore set forth, and which can be modified in avariety of ways within the scope of the following claims.

What is claimed is:

1. A controllable inductor including a ring core of magneticallypermeable and saturable material, and a generally H-shaped yoke ofmagnetically permeable material extending diametrically across from afirst side of the ring core to a second side of the ring core oppositeto said first side, the plane of the axes of the two parallel legs ofthe H-shaped yoke being generally perpendicular to the plane of the ringcore and with the inner surface of said first side of the ring corelying within one of the recesses of said H-shaped yoke and with theinner surface of said second side of the ring core lying within theother recess of the H-shaped yoke, a control winding around both of saidlegs of said H-shaped yoke and being encompassed by said ring core, anda signal winding in two parts connected in series and wound aroundportions of said ring core which are on opposite sides of said H-shapedyoke.

2. A controllable inductor as claimed in claim 1 and wherein saidgenerally H-shaped yoke is laminated, each lamination including aT-shaped part having a shank and two arms of unequal length extendingfrom opposite sides of the shank near one end, said arms being aligned 3one with the other and forming one leg of the generally H-shaped yokeand a straight part extending across the opposite end of the shank andparallel with the arms of the T-shaped part and forming the other leg ofthe yoke, the respective arms of the T-shaped part of at least onelamination being reversed in position with respect to the arms of theT-shaped part of another lamination, with opposite sides of the shanksof the respective reversed T-shaped parts being displaced towards theinner surface of the ring core at the respective first and second sidesthereof.

3. A controllable inductor comprising a continuous ring of ferritematerial forming a ring core, a yoke formed predominately ofmagnetically soft laminated material extending diametrically across themiddle of said ring core from one side to the other, said yoke beinggenerally H-shaped as seen looking parallel with the plane of said ringcore, with the central body portion of said H-shaped yoke extendingdiametrically across within the interior of said ring core and with thelegs of said H- shaped yoke overlapping opposite sides of the said ringcore in straddling relationship, a control winding around said yoke andencompassed by said ring core, and a signal winding around said ringcore outside of said control winding.

4. A controllable inductor comprising a closed loop of ferrite materialforming a closed core, a laminated H-sh aped yoke extending across themiddle of said closed loop core from one side to the other thereof, theplane of said H-shaped yoke being perpendicular with the plane of saidclosed loop core, opposite sides of said closed loop core extendingthrough the recesses at opposite ends of said H-shaped yoke and beingstraddled by the legs at opposite ends of said H-shaped yoke, saidlaminated H-shaped yoke including a plurality of 1aminations, eachlamination of said plurality being formed in two parts, one of which isgenerally rectangular and forming one leg of the H-shap ed yoke, and theother part being T-shaped, with the shank thereof forming the centralbody portion of the H-shaped yoke and with the two arms thereof formingthe other leg of the H-shaped yoke. I

5. A controllable inductor as claimed in claim 4 and wherein one armextending from one side of each of said T-shaped lamination parts islonger than the opposite arm.

6. A controllable inductor as claimed in claim 5 and wherein certain ofsaid T-shaped lamination parts are stacked in alternate directions andthe respective edges of the shanks thereof adjacent to the shorter armsare pressed firmly against the interior surface of the closed core.

References Cited in the file of this patent UNITED STATES PATENTS457,407 Spencer Aug. 11, 1891 1,585,389 Judd et al. May 18, 19-261,587,381 Hinsky June 1, 1926 1,601,400 Latour Sept. 28, 1926 2,374,059Wentz Apr. 17, 1945 2,471,411 Claesson May 31, 1949 2,818,514 Goertz eta1. Dec. 31, 1957 FOREIGN PATENTS 209,345 Great Britain 1 Jan. 10, 1924

